The Childhood Development after Cochlear Implantation (CDaCI) Study is a multisite, prospective investigation of a large and diverse cohort of US children with cochlear implants. Our primary objective is to evaluate the effect of variables that influence language learning after implantation. Success in spoken language depends on complex interactions between multiple domains of development. Thus, our aims are driven by hypotheses that relate variability in post-implant language outcome to environmental, social, interventional, and biological influences. A major challenge in childhood research relates to the reliable elicitation of communication and linguistic data. We address this task with hierarchical measures and videoanalytic techniques, recorded at fixed intervals, which allow us to track communicative skills as they emerge. We continue to build on this research experience to examine how language skills unfold in children participating in the study, evaluating their: 1) expressive and receptive language and academic achievement, 2) speech production, 3) speech recognition, 4) cognitive skills, 5) social interaction and behavior, 6) relationships with family members, and 7) health-related quality of life and related economic outcomes. CDaCI Study participants consist of children who received a cochlear implant (CI) before the age of 5 years (n=188) and a control group (n=97) of normal hearing (NH) age-mates. Average ages at enrollment were 2.2 years (CI) and 2.3 years (NH). Retention rates for ongoing data accrual are 85% for CI children and 84% for NH children, although all data collected over the past 8+ years have been included in published analyses. So, as CDaCI participants entered the study as preschoolers, they now embark on their middle school experience, entering high school over the next five years at current average ages of 11.0 (CI) and 10.8 (NH) years old. Despite wide recognition of the benefits of early cochlear implantation, there remains equipoise with respect to clinical, rehabilitative, and educational strategies that enable cochlear implant technology to be used to its fullest potential for language acquisition. Modifiers of linguistic outcome become even more compelling as children with cochlear implants face the communication and social demands of their early teens. This prospective, multidimensional study with concurrent controls offers prospects for novel, generalizable insights into the sources of variation in language learning and social and behavioral development after cochlear implantation, offering clinical guidelines to reduce low performance and variation in outcome.